Impact of Crop Rotations and Soil Amendments on Long-Term No-Tilled Soybean Yield

Continuous cropping systems without cover crops are perceived as unsustainable for long-term yield and soil health. To test this, cropping sequence and cover crop effects on soybean (Glycine max L.) yield were assessed. Main effects were 10 sequences of soybean, corn (Zea mays L.), and cotton (Gossypium hirsutum L.) grown on a Loring silt loam at the Research and Education Center at Milan (RECM), TN, and six cropping sequences of corn and soybean on a Maury silt loam at the Middle Tennessee Research and Education Center (MTREC), Spring Hill, TN. Sequences were repeated in 4-yr Phases (i.e., I, II, and III) from 2002 to 2013. Split-block treatments consisted of hairy vetch (Vicia villosa L.), Austrian winter pea (Pisum sativum L. sativum var. arvense), wheat (Triticum aestivum L.), poultry litter, and a fallow control. Continuous soybean yield was equivalent to all rotations (2.6 and 2.7 Mg ha(-1), respectively; P = 0.23), however, yield varied per phase (P < 0.001). Specifically, soybean yield in soybean-soybean-corn-cotton during Phase II and corncorn-soybean-corn during Phase I (4.2 and 4.1 Mg ha(-1), respectively) exceeded continuous systems during Phases II and III (P < 0.05). Poultry litter increased yield 11% across locations and years compared to wheat cover crops (P < 0.05). Incorporating corn once within a Phase increased yield 8% relative to continuous soybean, whereas cotton (once or twice) within a rotation had no effect. Consequently, including corn once within a 4-yr rotation and poultry litter improved soybean yields, albeit no mono-cropping yield penalties occurred long-term.